1. Field of the Invention
The present invention is concerned with a mechanical supercharger system to be used in an internal combustion engine.
2. Description of the Related Art
In an engine system with a mechanical supercharger the increased supercharge pressure has generally bad effects upon the longevity of the engine and the supercharger, and the driving load of the supercharger during running increases the fuel consumption. In order to minimize these conditions a by-pass valve system has been used so as to by-pass compressed air back to the suction inlet of the supercharger. However the by-pass valve system with by-pass pipes needs a large space and has been difficult to mount on the engine. Even if such mounting is possible, the pipes are long, and consequently the supercharger is not efficiently used.
A conventional turbo-supercharger with an air by-pass system (FIG. 4) is described in Japanese application JITSU-KAI-SHO 63-90033. There an air by-pass system of the supercharger 51 which by-passes the air downstream from the compressor 50 to a point upstream therefrom at the initial period of speed reduction includes a by-pass 52 and a by-pass valve 53 selectively closing the by-pass 52. A diaphragm 55 operates the by-pass valve 53 so as to open and close the by-pass valve in proportion to the pressure difference between the front and the back of the throttle valve 54. A relief passage 56 leaks pressure from a point downstream of the throttle valve 54 to the engine intake.
Because the by-pass valve 53 is separated from the supercharger to create two bodies, a large space is needed for the air passages. Therefore it is difficult to mount the system on the engine. Further because of the long length of the air passages, the air pressure losses increase. Therefore, when driving, the reduction of the driving load loss attributable to the supercharger which is made possible by the by-pass, is limited. Consequently, fuel consumption is made worse. Furthermore, resonance pulses in the long air by-pass passages case the flow resistance in the air by-pass passages to change cyclically. The pulsations have a bad effect upon the longevity of the valve seal of the by-pass valve and the spring.
The conventional mechanical supercharger in FIG. 5 is described in the Japanese application JITSU-KAI-SHO 63-11373. There, in the interior of the body 58 including the air compressor 57 for the charging air into the engine, a by-pass is provided so as to communicate between points upstream and downstream of the compressor 57. A control valve 59 is provided to open and close the by-pass. However, because of the length of the by-pass, the passage resistance increases, and consequently the fuel consumption is made worse.